Physical and Chemical Properties

Physical vs Chemical In Chemistry we focus on physical and chemical properties that help us organize Elements, chemicals, compounds, and everything in chemistry Physical Change – is when we are able to change the physical appearance of the substance. For example: the texture, size, colour, temperature, volume, shape, the state of the substance (solid, liquid, gas) are all physical changes. The same element or compound exists prior to, or after the physical change. I.E. the characteristics of the object remains unchanged. Example melting of wax, boiling of water, chopping wood, crumpling paper.

Physical Properties There are many different types of physical properties that help us to understand physical changes. Any changes to these properties are considered a physical change. Physical Properties: Colour State of matter Mass Density Solubility Melting Point/ Boiling Point Conductivity of Heat and Electricity Brittleness/ Hardness\ Magnetism Viscosity Malleability Ductility Lustre

States of Matter There are three states of physical properties: 1) Solid – ex. rock, table, glass, tree and etc… 2) Liquid – ex. water, pop, tea, soup and etc… 3) Gas – ex. oxygen, propane, helium, hydrogen and etc… The changes of states go from solid  liquid  gas and can go from gas  liquid  solids. They can only change in this order. Thus, the ability to change from one state to another depends on an objects melting and boiling points.

States of Matter As stated earlier, substances can change from solid  liquid  gas and can go in reverse order from gas  liquid  solids. When a substance goes from solid  liquid  gas, heat has to be added at each stage. When a substance goes from gas  liquid  solid, heat has to be removed.

Melting and Boiling Point Melting point – the temperature needed for a substance to change from solid to a liquid. Ex. Pure water melts at 0º Celsius. Thus, it freezes just below 0º Celsius. Boiling point – the temperature needed for a substance to turn from liquid to gas. Ex. Pure water boils at 100º Celsius and the gas will turn to liquid just below 100º Celsius.

Melting and Boiling Point Pure Substance Melting Point (◦C) Boiling Point (◦C) Carbon (diamond) 3350 4830 Chlorine -101 -34 Copper 1085 2580 Gold 1065 2710 Iron 1540 2890 Magnesium 650 1120 Mercury -39 357 Oxygen -218 -183 Sodium 98 890 Sodium Chloride 808 1465 Water 100

Density Density – the heaviness of a substance is density. We do not have a device to measure density, we can only calculate it. Density equation Density = mass volume The unit of density is measured in g/cm3 or g/ml. Note, 1 ml = 1 cm3 The image on the right from top to bottom goes from lightest to heaviest material.

Density Density example: A piece of aluminum has a mass of 20g and has a volume of 7.4 cm3. What is the density of aluminum? Density = 20 g = 2.7 g/cm3 7.4 cm3 Note, no matter how much aluminum you have the density will stay the same; increase the mass, you increase the volume and the density stays the same. Density is a constant, it never changes.

Density Density example #2 Glycerol is a liquid and thus we cannot measure its cm3, we have to measure it in ml. If you have 1500 grams of glycerol and a volume of 1190 ml, what is its density? Density = 1500 g = 1.26 g/ml 1190 ml

Other Important Physical Properties Malleability – the ability to change its shape. Ex. Playdough, we can flatten it by applying pressure to it, and if we roll it together it can thicken it up. Ductility – It references the softness of a metal. The ability to strip away, twist, and bend the metal. Ex. Gold is very ductile as it can be squeezed and bent and twisted. Solubility – The degree to which a substance will dissolve in a given amount of another substance. Ex. Copper Chloride into water. Conductivity - The ability of a material to conduct electricity or heat. Metal wire (copper or aluminum) are good conductors,. Non metal (carbon, oxygen) are good non-conductors.

Chemical Properties Chemical Changes – is when you are able to take a substance and completely change it into another substance. Chemical properties are used to group substances that have common chemical reactions. There are four signs that a chemical change has taken place. A color change takes place Heat, light or sound is produced Bubbles or a gas is formed A precipitate forms

Colour Change The rusting of Iron produces a colour change from silver to red that is caused by a chemical reaction . 4Fe(s) + 3O2(g) + 6H2O (l) → 4Fe(OH)3 (s) Rusted Iron Non Rusted Iron

Bright Light/Heat Take Magnesium and burn it – it produces a bright light. This bright light indicates a chemical reaction has occurred. 2Mg(s) + O2(g) ---> 2MgO (s)

Bubbles or Gas Many different chemical reactions are done to produce gas (oxygen, hydrogen, nitrogen, hydrogen). Zinc and hydrochloric acid release hydrogen. Zn(s) + HCl(l)  ZnCl2(aq) + H2 (g)

Precipitate When we take Silver Nitrate and add it to Sodium Chloride we produce a solid precipitate - Silver Chloride – and an aqueous solution of Sodium Nitrate. AgNo3 (aq) + NaCl (aq)  AgCl (s) + NaNo3 (aq)

Chemical and Physical Changes Physical changes are: Usually reversible No new substance is formed Properties do not change Energy change may occur, but it is really small and usually non-noticeable. Chemical changes are: Usually irreversible Produce new substances (a gas or liquid) Create a new set of properties (a new colour) Energy change may occur (releasing heat or absorbing heat)

Example of Physical and Chemical Changes Physical Change Chemical Change When cream is whipped, air puffs up the cream. The substance is still cream. Baking powder reacts with heat to produce carbon dioxide which makes bread rise. Boiling water creates a gas, but the gas created is still water. Gasoline burns to create heat, carbon dioxide and water. New gases are created as well. Sugar dissolves in water. The sugar may “disappear”, but if you vaporize the water you will be left with sugar crystals. If you drink it the water and sugar you will still taste the sweetness. Sunlight on the skin creates vitamin D and melanin in the skin. Tattoo ink is injected into the skin to create a graphic. Even when the ink is injected into the skin, it is still ink. Hydrogen peroxide is used to bleach hair to a much lighter colour. The hair colour changes into another substance that has less, or no, colour.

Assignment Pg 164 Questions – 1, 3 – 9 , 12 – 13 Pg 170 Questions – 1 – 9, 12 (challenging)